1. Field of the Invention
This invention relates to a wafer pod and, more particularly, to a wafer pod provided with wafer holding device for retaining securely the wafers inside the wafer pod.
2. Description of the Related Art
It is well known that a wafer pod is always applied to store and preserve the wafers used in a semiconductor processing system. The object is to prevent the wafers from being damaged by equipments or other machines or polluted by particulate release or dust during transportation. To achieve the object, the wafers must be held securely within the wafer cassette inside a wafer pod.
As shown in FIGS. 1A and 1B, a conventional wafer pod 10 is mainly composed of a hollow housing 11 and a base 22 upon which a wafer cassette 21 for storing a plurality of wafers is mounted. When the hollow housing 11 and the base 22 with the wafer cassette 21 are together equipped, the hollow housing 11 receives the wafer cassette 21 and the room there between is made airtight.
Again considering the wafer pod 10, one can note that a first retaining mechanism 12 and a second retaining mechanism 13 are also provided. They are provided here to retain securely the wafers 23 in the wafer cassette 21 such that the wafers 23 would not move due to any vibration or shake of the wafer pod 10 and therefore the damage and particulate release of the wafers 23 can be avoided.
Referring to FIG. 1B, the retaining mechanisms 12 and 13 are actually linkage mechanisms including four-bar and five-bar types. When the housing 11 and the base 22 are together equipped, the base 22 contacts and forces the retaining mechanisms 12 and 13 such that the link-bars neighboring the wafers 23 contact and securely retain the wafers 23 in the wafer cassette 21.
However, for this wafer pod 10, there are still problems in totally preventing the wafers from being damaged by equipments or polluted by particulate release. As we can see, the movement of the link-bars neighboring the wafers 23 is not in a direction parallel to the plane surface of the wafers 23 or perpendicular to the edge surface of the wafers 23. This can cause the wafers 23 to quiver and rub against the link-bars neighboring the wafers 23 and therefore results in damages to and undesired particulate release from the wafers 23.
In view of this, an improved wafer pod with wafer holding device is disclosed. The proposed wafer holding device is characterized in that the wafers are retained securely by applying forces parallel to the edge surface of the wafers stored in the cassette when the housing and the base are equipped together.